Animal litters such as cat litter have been made out of a variety of absorbent materials. Early litter compositions used non-gelling or non-clumping clays, such as montmorillonite and attapulgite. Later, gelling clays, such as sodium bentonite, were used to absorb urine waste into a removable clump. The ability to scoop out all solid waste together with clumps of litter containing urine provided a cleaner litter box and reduced odor.
Litters made entirely from clay such as sodium bentonite have high bulk densities, in the range of 50-65 lbs/cu-ft., making them heavy and therefore difficult and costly to handle, package and transport. Attempts to address this problem by encapsulating particles of lighter weight clays with a coating of heavy, clumping clay like sodium bentonite have produced only marginal reduction in bulk density, to only slightly less than about 60 lbs/cu-ft. Also, the clump formation or strength of the clump for litters primarily made with sodium bentonite may be reduced due to salts and other constituents in animal and in particular cat urine that affect the gelling or clumping of these types of litters.
As an alternative to clays, certain plant-based, organic materials have been used to prepare absorbent granules, which can provide litter of somewhat lower bulk densities. Such materials also have the advantage of providing a recycling stream for materials normally treated as a waste by-product. Examples of such organic materials are wheat grain and by-products from wet milling of corn. Such organic materials however generally do not exhibit good clumping performance, even when containing starch, which has some limited function as a clumping promoter.